subtotal, submean, aggregate
Create another variable that gives the run number and aggregate on both the habitat and run number removing the run number after aggregating: runno <- cumsum(c(TRUE, diff(as.numeric(transect[,2])) !=0)) aggregate(transect[,1], list(obs = transect[,2], runno = runno), sum)[,-2] This does not give the same as your example but I think there are some errors in your example output.
On 2/26/06, Patrick Giraudoux <patrick.giraudoux at univ-fcomte.fr> wrote:
Dear All,
I would like to make partial sums (or means or any other function) of
the values in intervals along a sequence (spatial transect) where groups
are defined.
For instance:
habitats<-rep(c("meadow","forest","meadow","pasture"),c(10,5,12,6))
observations<-rpois(length(habitats),2)
transect<-data.frame(observations=observations,habitats=habitats)
aggregate() is not suitable for my purpose because I want a result
respecting the order of the habitats encountered although they may have
the same name (and not pooling each group on each level of the factor
created). For instance, the output of the ideal function
mynicefunction() would be something as:
mynicefunction(transect$observations, by=list(transect$habitats),sum)
meadow 16
forest 9
meadow 21
pasture 17
and not
aggregate(transect$observations,by=list(transect$habitats),sum)
Group.1 x
1 forest 9
2 meadow 37
3 pasture 17
Did anybody hear about such a function already written in R? If no, any
idea to make it simple and elegant to write?
Cheers,
Patrick Giraudoux
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